This invention relates to improvement in drill bits for through-the-steel drill stems of which the drill bit of our co-pending application Ser. No. 746,804, now U.S. Pat. No. 4,605,079, is a precursor. The invention was primarily developed in connection with mine roof drilling and it is thus described herein. However, it will be readily appreciated that our improved drill bit may be used with equal facility for other drilling operations, and description of the same in relation to mine roof drilling is not to be construed as a limitation on the scope of the invention.
In mining operations, such as coal mining, it has become a widely accepted practice to support the mine roof by means of roof bolts as embedded within spaced apart holes drilled in the mine roof. Roof bolts serve to pin pieces of loose material to solid rock above, reinforce areas of the underground arch, prevent sheet movement of rock strata, and form a solid self-supporting beam of several weak strata. With each advance of the mine face additional roof bolts are required and it thus follows that there will be an extremely large number of holes drilled into the mine roof for receiving roof bolts.
It is quite naturally desirable to prevent fine respirable dust from being suspended in the air the miners must breathe. As is obvious, drilling in a mine roof is a setting conducive to dispersion of drill dust within the mine. Through-the-steel drilling is thus usually used for drilling in mines. That is, use of a hollow drill stem in which a partial vacuum is created for drawing drill cuttings thereinto and thence to a collector. Drill bits for through-the-steel drill stems are provided with drill ports through which the drill cuttings may be drawn into the through-the-steel drill stem.
Others have previously proposed various types of drill bits for use with through-the-steel drill stems. By way of examples, as shown in U.S. Pat. Nos. 3,187,825; 3,434,553; 3,434,554; 3,613,807, 4,313,506; 4,330,044; and 4,492,278.
Drill bits of this type usually fall in the direction of those providing appropriate work surfaces, such as those of U.S. Pat. Nos. 4,313,506 and 4,492,278, or of those providing appropriate drill ports, such as that of U.S. Pat. No. 4,330,044.
As a subsequent improvement to the drill bit as shown in our co-pending application Ser. No. 746,804, now U.S. Pat. No. 4,605,079, we have found that a bit of this type having opposed hemispheric or radial cut drill ports opening to the bore from the drill tip and opening from the periphery of the bit and directly into the bore below the drill tip provides a bit having both an appropriate work surface and appropriate drill ports.
It is thus a primary object of this invention to provide a drill bit including a web for supporting a drill tip and in which the drill ports are contoured as a hemisphere with respect to opposed axially extending faces of the web, are open to the bore from the drill tip and extend axially along the bit and open from the periphery thereof to the bore below the web.
Our improved drill bit is preferably configured to receive a sleeve as designed to be indexed thereon with respect to the drill ports in a manner to delimit the same in somewhat the same manner as shown and described in our co-pending application Ser. No. 746,804.
Other objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, and in which drawings: